Lecture 4: Marine Fossils, geologic time scale Corresponding Reading Material ~ Lab Manuel: Marine Fossils ~ Levinton:chapters 2 and 3

Evidence for Evolution Similar life forms that are related Vestigial traits and homologous characters Evidence from the fossil record ~fossils are any trace of an organism that lived in the past. Fact of extinction Environmental change Plate tectonics

Geological Time Scientists have divided time since the formation of the Earth into a geological time scale. Each period has characteristics or events that are unique to them.

How do we know the age of the Earth?? During Darwin’s time, the Earth was thought to be 6,000 years old. Why?? Moon rocks and meteorites Theory of uniformitarianism states that geological process that are occurring today were the same in the past.

Relative vs Absolute Dating Relative Dating = refers to the determination of the age of a rock or geological sample by comparing its position to the position of other samples. Absolute Dating = refers to the determination of the age of a geological sample by calculations or radiometric decay and/or its position in relation to other samples

Dating Techniques Radiometric Dating = the process of determining the age of rocks by observing the ratio of unstable radioactive elements to stable decay products ~ Half-life = is the time it takes for one half of all the unstable nuclei in a sample to decay. During this process the radioactive element becomes a new element.

Dating Techniques Paleomagnetism = is the remnant magnetic field of a rock ~Tiny particles of iron-bearing minerals are present in balsamic rocks ~ These particles align with the Earth's magnetic field at the time they are formed and freeze in place as the rock solidifies ~ In the last 26 mill yrs, the poles have reversed 48 times. ~ This techniques is used to calibrate the geological time scale and to reconstruct continents

Dating Technique

Dating Technique

How Are Fossils Made? There are five ways an organism can become fossilized: 1. Permineralization (Petrification) = this process involves the replacement of the original organic tissues w/ minerals from the surrounding rock, including silica, calcite, or pyrite 2. Unaltered Preservation = occurs when the organism is preserved in its original state and is protected from the affects of permineralization (Ex: Insects which become trapped in tree sap which turns into amber) 3. Carbonization (Coalification) = results form the removal of all but the carbon elements (other elements such as hydrogen, oxygen, and nitrogen are removed) Trilobite Fossil

How Are Fossils Made? 4. Authigenic Preservation = these fossils are mold and casts or organisms which have dissolved or rotted away, leaving only a trace of their existence (the parts of the organism that are replaced are usually the hard parts of the dead organism) 5. Recrystalization = occurs when crystals form within the original structure, eventually replacing it and resulting in a crystallized copy Horn Coral Fossil Brachiopod Fossil

Pictures of Fossils Sponge Fossil Eocene Fish Fossil Ammonite Fossil (Jurassic Period) Tuzoia Fossil

Fossils Over Time Below the chart shows when different organisms appear within the fossil record.

Burgess Shale Fossil The Burgess Shale is is an exceptional Middle Cambrian age (~540 mya) fossil locality located in Yoho National Park in the Rocky Mountains near Field, British Columbia, Canada. It is special because of the soft-bodied preservation of a wide variety of fossil invertebrate animals.